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Hi Guys. I've been through a pretty frustrating "Increased Emmission" episode... and have replaced the PCV valves and Thermostat... to no avail. Finally got a reader and found that the vapor pump was reading bad... but not really. Bottom line, seems the gas cap was leaking a bit which made it think it was the pump. Code was 1434 but the pump seemed to be operating correctly so Gas Cap. It looked fine so I never heeded the warnings about it being a culprit. But then I was filling up and I notice that it bottomed out when closing it. What I mean by that is that the screw action was stopped by the tabs hitting their stops before the gasket fully seated. In essence, the tabs, or the ramps had worn enough (or the tabs bent from overtightening) that the gasket was no longer pulled in for a good seal. So I decided to get a new gas cap. After one out of stock shop, I asked the wife to get one at the dealer on her way home from work. And of course she forgot... several times! I was about to go down to get one myself when I thought what the hell, I'd try to fix this cap. And indeed, I did and it only took about 10 minutes. Here is how it was done:

First: Remove the cap. Mine is a 645ci but I'd bet this is the same for many BMWs. I'd post pictures, but the image button seems to require me to host pictures and I don't have a host set up. I'll try verbally ... (figured it out by against all my natural instinct..... reading the instructions...)

Slide the rubber lasso out of the keyhole to release the cap from the car.

Take the post off the center of the cap. This is the green thing in the middle of the cap used to put your cap in the holder while you fill. Just pry it out with a screwdriver by inserting it between the tab and this plastic thing. It is held in by the ring of metal of the center of the cap and is just a pressure fit. (I note that this isn't always green, but it is the post thing in the center of the inside of the cap).

Remove the cap handle. This is the ratcheting thing that you grip the cap with to open and close it. There are four tabs in the plastic that go over the edge of the metal frame of the cap. Just pry these off with your fingers. I was able to pop this off without any fuss at all. At this point, you have just the metal core of the cap.

Optional: Remove the gasket. I took out my gasket and reversed it. This just prys out by slipping a screwdriver between it and the metal body and prying it out.

The Key Step: You are now going to bend the tabs that screw into the filler pipe of the car. What I did was take two 3/8" sockets for 1/4" drive and rested them in the curved cradle of these tabs. Then I positioned the whole thing in my vise. I then tightened the assembly slightly so that the vise held it all together. Now I slid the sockets outward so they were in the end of the metal tabs. With everything positioned, I turned the vise gently and bent these wings in about a millimeter.

Put the whole thing back together and it tightens in a whole new way. I've reset the light, and am free of the emissions light.

Hope this saves someone else some frustration.

Had a thought of why this could happen... I think if one over-tightens the gas cap, one can bend these tabs. Moral of the story is turn till it clicks and no more.